1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device in which light shielding property of a thin film transistor portion is enhanced.
2. Description of the Related Art
A liquid crystal display device has features of being slim and lightweight, consuming low power, and the like. An active matrix liquid crystal display device which uses a transistor characteristically has a large contrast and high response speed, and thus is widely used in a television, a personal computer, a portable electronic device, or the like. Moreover, in recent years, along with improvements made in luminance, definition, and color purity of the liquid crystal display device, high performance has been required for the liquid crystal display device. As the transistor used in the liquid crystal display device, there is employed a thin film transistor (TFT) in which a transistor is formed on a silicon thin film. In the active matrix liquid crystal display device using the TFT, when light output from a light source or ambient light enters a channel region of the TFT, a leak current flows due to the entering light, which changes TFT characteristics to degrade display quality thereof. In order to solve the above-mentioned problem, there is known a method of disposing a lattice-like light shielding film around respective pixel portions so that light does not enter the TFT. An example of the liquid crystal display device as described above is illustrated in FIG. 1 and FIG. 2.
FIG. 1 is a cross-sectional view in which an enlarged cross-section of a TFT element is illustrated. FIG. 2 is an enlarged plan view illustrating a part of a group of adjacent pixels in a liquid crystal display device in which a data line, a scanning line, a pixel electrode, a light shielding film, a color filter, and the like are formed. A color filter substrate 1 includes a light shielding film 5 for shielding light at a boundary between pixels, a color filter 6, and a common electrode 8 on a side of a glass substrate 3 in proximity to a liquid crystal layer 15. The color filter 6 generally is formed of a red-colored layer (R), a green-colored layer (G), and a blue-colored layer (B) which are three primary colors of light. On a TFT array substrate 2, on a side of a glass substrate 4 in proximity to a liquid crystal layer 15, a plurality of scanning lines 9 and a plurality of signal lines 12 are provided so as to intersect each other, thin film transistors (TFTs) 16 are each disposed at a portion in which the scanning line 9 and the signal line 12 intersect each other, and pixel electrodes 14 each connected to the TFT are disposed. The color filter substrate 1 and the TFT array substrate 2 sandwich a liquid crystal layer 15 therebetween, and a periphery of a display unit is sealed, to thereby form the liquid crystal display device.
The TFT 16 disposed on the TFT array substrate 2 includes the scanning line 9, an insulating film 10, a semiconductor layer 11, and the signal line 12 and a drain electrode 13 which are connected to the semiconductor layer 11. The drain electrode 13 is connected to the pixel electrode 14, and liquid crystal is driven by means of an electric field formed between the pixel electrode 14 and a common electrode 8.
Conventionally, a backlight A of the liquid crystal display device passes through an aperture of a pixel, and then is reflected on the light shielding film 5 of the color filter substrate 1, thereby entering the TFT 16 disposed on the TFT array substrate 2. Accordingly, there is a problem in that a leak current generated by the light entering the TFT 16 changes TFT characteristics, and a contrast of a display image is lowered, which degrades the display quality. In order to solve this problem, there is known a method in which reflected light caused by the light shielding film 5 is reduced with the use of the color filter 6, an amount of light entering the TFT is reduced, whereby the leak current is prevented to maintain the display quality. Further, it is known to use a colored layer pattern of colors which sufficiently absorb short-wavelength light as colored layers of the color filter disposed on the light shielding film 5, whereby the leak current is effectively suppressed (for example, see JP 2001-91971 A).
In recent years, along with an increase in light amount of backlight for displaying a bright image, countermeasures against the leak current caused by light have been increasingly important.